Required roles: broadband-r

Optional roles: pricing-r

Returns the contract for the given connection, including its active contract lines.

Historic contract lines are omitted. As the contract lines contain pricing details, they are
only returned when the user has the pricing-r role for the connection's organization;
otherwise contract_lines is null.

On a contract line, sales_price is the monthly price of a single unit, period_price the price of
a single unit for a full billing period (sales_price × period, null for one-off lines) and
total_price the amount charged per billing period for the full quantity.